1. Field of the Invention
The field of the present invention is that of fuel compositions and particularly fuels intended for use in heat engines. More precisely, the fuels envisaged within the framework of the invention contain predominantly liquid hydrocarbons and especially:
those of mineral origin, such as petroleum derivatives of the types comprising petrols, diesel fuels, kerosenes and heating oils, and/or such as those derived from coal or gas (synthetic engine fuels); PA1 those of vegetable origin, such as esterified or non-esterified vegetable oils; PA1 and mixtures thereof. PA1 .fwdarw.this emulsion contains an emulsifying system comprising: PA1 .fwdarw.this emulsifying system has an overall HLB of between 6 and 8, preferably of between 6.5 and 7.5; PA1 .fwdarw.and the emulsion is prepared in such a way that the mean size of the droplets of aqueous disperse phase is less than or equal to 3 .mu.m, preferably 2 .mu.m and particularly preferably 1 .mu.m, with a standard deviation of less than 1 .mu.m. PA1 the dimensional profile of the droplets of aqueous phase PA1 and the inventive choice of an appropriate composition for the emulsifying system are very clearly differentiated from the invention according to WO 93 18 117, which is improved by the present invention. PA1 (I) from 2.5 to 3.5 parts by weight, preferably 3 parts by weight, PA1 (II) from 1.5 to 2.5 parts by weight, preferably 1.5 to 2 parts by weight, PA1 (III) from 0.5 to 1.9 parts by weight, preferably 0.5 to 1.5 parts by weight. PA1 hydrocarbon(s) 50 to 99%, preferably 65 to 99%, PA1 water 0.1 to 50%, preferably 1 to 35%, PA1 emulsifying system 0.05 to 5%, preferably 0.1 to 3%, PA1 additives 0.01 to 5%, preferably 0.05 to 2%. PA1 the emulsifying system described above PA1 and optionally at least one other additive preferably selected from the products described below, namely: cetane improvers, catalytic promoters of soot combustion, biocides, detergents, ammoniated compounds, antifreezes, esterified or non-esterified vegetable oils, and mixtures thereof. PA1 a--taking at least one hydrocarbon, water and an emulsifying system comprising: PA1 b--mixing these constituents to form a water-in-oil emulsion; PA1 c--and fractionating the emulsion to reduce the size of the droplets of aqueous disperse phase to a mean size less than or equal to 3 .mu.m, preferably 2 .mu.m and particularly preferably 1 .mu.m, with a standard deviation of less than 1 .mu.m. PA1 (I) from 2.5 to 3.5 parts by weight, preferably 3 parts by weight, PA1 (II) from 1.5 to 2.5 parts by weight, preferably 1.5 to 2 parts by weight, PA1 (III) from 0.5 to 1.9 parts by weight, preferably 0.5 to 1.5 parts by weight.
The present invention relates more specifically to novel fuel compositions consisting of emulsions of water in at least one hydrocarbon and generally in a mixture of hydrocarbons, for example the mixture of which diesel fuel is composed.
The present disclosure will therefore deal with stabilized water/hydrocarbon emulsions comprising surfactants capable of emulsifying and of stabilizing such emulsions.
The present invention further relates to a method of preparing emulsified water/hydrocarbon fuels (e.g. engine fuels) combined with one or more surfactants.
2. Description of Related Art
The present invention comes within the field, which has long been fashionable, of developing fuel compositions, especially engine fuel compositions, comprising substitute products for petroleum derivatives, with the aim of reducing costs and limiting pollution.
Water was very quickly found to be a valuable additive or partial substitute for petrol or diesel fuel. Water is in fact an inexpensive and non-toxic liquid which has proved capable of reducing fuel consumption and the emission of visible or invisible pollutants.
Despite all these assumed advantages, no water/hydrocarbon engine fuel has yet been used industrially, on a large scale, in concrete applications because of prohibitive difficulties with their processing and use.
According to a first approach, it has been envisaged to make provision for storing water and fuel separately on the vehicle and mixing them at the time of use. This approach requires the installation, on board the vehicle, of a complex and sophisticated device for carrying out specific mixing and metering operations. The cost, bulk and delicacy of such devices have proved totally dissuasive in the development of this approach.
The second ponderable approach consists in using ready-made mixtures of water and fuel, but this did not reckon with the considerable problems of the storage stability of such mixtures at temperatures ranging from -20.degree. C. to -70.degree. C., and of the stability of the emulsion in a tank under use conditions.
Thus there are many unfruitful technical proposals which aimed, in vain, to provide emulsified engine fuels comprising water and, more generally, novel non-polluting engine fuels resulting in low consumption.
As an illustration of one such prior art, there may be mentioned French patent application Ser. No. 2 470 153, which discloses an emulsified engine fuel comprising hydrocarbons, water, an alcohol (methanol, ethanol) and an emulsifying system formed of sorbitan monooleate and ethoxylated nonylphenol. The concentration of the emulsifying system in the emulsion is between 3 and 10% by volume. The essential presence of alcohol in this emulsion constitutes an extremely penalizing factor, especially as regards the economics and the engine performance characteristics capable of being obtained with this emulsion. Moreover, it should be noted that the stability of this water-alcohol/hydrocarbon emulsion leaves something to be desired. In fact, after the emulsion has been stored for 72 hours, which corresponds to a realistic period of non-use of a vehicle running on this fuel, there is an incipient phase separation (dephasing/demixing) between the hydrocarbons and the aqueous-alcoholic mixture. The hydrocarbons dephased (separated out) at the end of this time can represent up to 3% by volume of the emulsion. It is easy to imagine that, after a few days' storage, the dephasing of this emulsion according to patent application No. 2,470,153 is sufficient to prohibit the running of the vehicle under normal conditions of application.
U.S. Pat. No. 4,877,414 has further disclosed an emulsified engine fuel containing a number of additives, including an emulsifying system formed of sorbitan sesquioleate, sorbitan monooleate and the polyoxyethylene ether (6 EO) of dodecyl alcohol. Preferably, according to said patent, the total concentration of all the additives is about 2.1%. The other additives which can be employed apart from the emulsifying system are a mono-.alpha.-olefin (1-decene), methoxymethanol, toluene, an alkylbenzene and calcium hydroxide. This formulation is extremely complex, if only for the number of additives employed. It is also relatively expensive. Finally, the emulsified fuel according to said patent again suffers from a lack of stability, particularly at low temperature. The Applicant was moreover able to demonstrate this clearly by reproducing the preferred embodiment of the emulsified fuel according to said U.S. patent. It was found that the emulsion separates (dephases) in one hour. The phenomenon is further exacerbated at low temperatures below 5.degree. C. It is therefore hardly imaginable what might happen in vehicle tanks containing this emulsion when placed under real winter use conditions.
The abstract of Japanese patent no. 77-69 909, given in Chemical Abstract 87 : 138 513 x, relates to an emulsified engine fuel (kerosene/water) comprising sorbitan sesquioleate and the polyethylene glycol ether of nonylphenol as emulsifiers. The size of the droplets of aqueous disperse phase is .ltoreq.20.mu. with a mean value of the order of 10.mu.l. This technical proposal is again incapable of suitably satisfying the objectives of physicochemical stability, limitation of pollution, cost reduction and reduction of fuel consumption. This technical teaching can therefore provide no help for those skilled in the art working in the prospective field of the invention.
Another Chemical Abstract, no. 101 : 57 568 z, summarizing Brazilian patent no. 82 4 947, relates to an emulsified fuel comprising hydrocarbons consisting of extremely viscous and heavy petroleum derivatives, water, ethanol and an emulsifier consisting of ethoxylated nonylphenol. This emulsified fuel is intended for use in conventional furnaces and heating oil burners. This fuel cannot meet the expected performance specifications of combustion, limitation of pollutants and low consumption. Moreover, the physicochemical stability of this emulsion is poor.
PCT international patent application WO-93/18117, in the name of the Applicant, describes emulsified fuels which the present invention proposes to improve.
These emulsified fuels, which can be engine fuels, comprise specific amounts of hydrocarbons and a minor amount of a group of additives, including especially an emulsifying system comprising sorbitan oleate, polyalkylene glycol and alkylphenol ethoxylate. The disperse phase of these emulsified fuels consists of water present in a proportion of 5 to 35% by weight, while the additives are present in a proportion of 0.1 to 1.5% by weight.
The concentration ranges (in % by weight) of sorbitan oleate, polyalkylene glycol and alkylphenol ethoxylate are respectively 0.20-0.26/0.20-0.25/0.20-0.27. The entire patent application states that these three principal additives are used in equal amounts: 1/1/1.
The performance characteristics of these known emulsified fuels, in terms of stability, reduction of visible and invisible pollutants, reduction of consumption and cost reduction, are totally capable of improvement. In particular, research and development on these emulsified engine fuels has made it possible to show that improvements in terms of the cost and stability of the emulsion are desirable, especially under real use conditions in a vehicle.
This review of the prior art has shown that there is an unsatisfied need for an emulsified fuel which is physicochemically stable (no dephasing), creates low pollution, is economical and reduces consumption.
Confident of this observation, the Applicant therefore set itself a number of objectives, which will be listed below.
One of the essential objectives of the present invention is to rectify this omission by providing an emulsified fuel, particularly an engine fuel, formed of a stable water/hydrocarbon emulsion which remains perfectly homogeneous over long periods of time, both in storage tanks and in elements of the circuits making up the combustion devices in which said fuels may be used.
Another essential objective of the present invention is to provide novel improved emulsified engine fuels which give good results in terms of reducing the fuel consumption and reducing the emission of visible pollutants, i.e. smoke and solid particles, and gaseous invisible pollutants such as CO, NO.sub.x and/or SO.sub.2, unburnt hydrocarbons and CO.sub.2.
Another essential objective of the present invention is to provide novel emulsified fuels which have a low cost price so as not to wipe out the advantage gained by the partial replacement of expensive hydrocarbons with water.
Another objective of the present invention is to provide a method of preparing stable, non-polluting and economical emulsified fuels, it also being necessary for said method to be inexpensive and furthermore easy to carry out, without a sophisticated operating protocol or device.
In said context, the Applicant pursued its inventive efforts and developed novel improved emulsified fuels, the original features being as follows:
On the one hand the fuels have an aqueous disperse phase consisting of droplets of reduced size which possess an interfacial film for dealing with the phenomenon of coalescence. It is also essential, in terms of the stability of the emulsion, for the size distribution of the water droplets to be as narrow as possible.
On the other hand the chosen composition of the emulsifying system is a contributing factor in achieving the specifications of stability, size and size distribution droplets of the aqueous phase in the diesel fuel phase.